Microreactor comprising a porous ceramic material

Abstract

Product formed from a ceramic material, at least part of the product not being formed from amorphous silica, having pores and satisfying the following criteria: (a′) at least 70% by number of the pores are tubular pores extending substantially parallel to each other in a longitudinal direction; (b′) in at least one cross-section plane, at least 30% by number of the pores have a section of convex hexagonal shape, these pores being known hereinbelow as “hexagonal pores”, at least 80% by number of the hexagonal pores having a roundness index of greater than 0.70, the roundness index being equal to the ratio SA/LA of the lengths of the small and long axes of the ellipse in which the section is inscribed; the mean size of the cross sections of the pores is greater than 0.15 μm and less than 25 μm.

1 . A product formed from a ceramic material, at least part of said product not being formed from amorphous silica, comprising pores and satisfying the following criteria:
 at least 70% by number of said pores are tubular pores extending substantially parallel to each other in a longitudinal direction;   in at least one cross-section plane,
 at least 30% by number of the pores have a section of convex hexagonal shape, these pores being known hereinbelow as “hexagonal pores”, at least 80% by number of said hexagonal pores having a roundness index of greater than 0.70, the roundness index being equal to a ratio SA/LA of lengths of small and long axes of an ellipse in which said section is inscribed; 
   mean size of the cross sections of said pores is greater than 0.15 μm and less than 25 μm.   
     
     
         2 . The product according to  claim 1 , the ceramic material being chosen from the group formed by zirconium oxide, partially stabilized zirconium oxide, stabilized zirconium oxide, yttrium oxide, doped yttrium oxide, titanium oxide, aluminosilicates, cordierite, aluminium oxide, hydrated aluminas, magnesium oxide, talc, nickel oxide, iron oxides, cerium oxide, doped cerium oxide, oxides of perovskite structure, compounds comprising titanium of the type La 4 Sr 8 Ti 11 Mn 1-x Ga x O 38  with 0≦x≦1 and La 4 Sr 8 Ti 12-n Mn n O 38  with 0≦n≦1, compounds of the type BaTiO 3 , BaZrO 3 , Pb(Mg 0.25 Nb 0.75 )O 3 , Ba(Zn 0.25 Nb 0.75 )O 3 , Pb(Zn 0.25 Nb 0.75 )O 3 , PbTiO 3 , CaCu 3 Ti 4 O 12 , compounds of bimevox-type structure, compounds of lamox-type structure, compounds of the type SrCe 1-x M x O 3  with 0≦x≦1 and M being a rare-earth metal, compounds of the type BaCe 1-x M x O 3 , with 0≦x≦1 and M being a rare-earth metal, compounds of the family La x Sr 1-x ScO 3  with 0≦x≦1, zeolites of structure Na x1 Ca x2 Mg x3 Ba x4 K x5 Al x6 (Si x7 O x8 ),x9H 2 O, x1 to x9 being positive integers or zero satisfying the following conditions: x6>0, x7>0, x8>0, x9>0 and x1+x2+x3+x4+x5>0, silicon carbide, silicon nitride, boron nitride, boron carbide, tungsten carbide, molybdenum disilicide MoSi 2  and titanium boride TiB 2 , and mixtures thereof. 
     
     
         3 . The product according to  claim 1 , in which at least 80% by number of said pores that have a section of convex hexagonal shape in said transverse plane have a roundness index of greater than 0.75. 
     
     
         4 . The product according to  claim 1 , in which, in the said cross-section plane, at least 50% by number of the pores have a section of convex hexagonal shape. 
     
     
         5 . The product according to the  claim 4 , in which, in said cross-section plane, at least 90% by number of the pores have a section of convex hexagonal shape. 
     
     
         6 . The product according to  claim 1 , in which, in said cross-section plane, the mean pore size is greater than 0.25 μm. 
     
     
         7 . The product according to  claim 6 , in which, in said cross-section plane, the mean pore size is greater than 1 μm. 
     
     
         8 . The product according to  claim 1 , in which, in said cross-section plane, the mean pore size is less than 20 μm. 
     
     
         9 . The product according to  claim 8 , in which, in said cross-section plane, the mean pore size is less than 10 μm. 
     
     
         10 . The product according  claim 1 , in which at least 70% by number of the pores are frustoconical tubular pores opening at their two ends with wide and narrow apertures, respectively, known as “through-pores”, a ratio of a mean equivalent diameter of the narrow apertures to a mean equivalent diameter of the wide apertures of said through-pores being less than 0.95. 
     
     
         11 . The product according to  claim 1  which has been sintered. 
     
     
         12 . A device comprising a product according to  claim 1 , impregnated with an impregnation material chosen from zirconium oxide, partially stabilized zirconium oxide, stabilized zirconium oxide, yttrium oxide, doped yttrium oxide, titanium oxide, aluminosilicates, cordierite, aluminium oxide, hydrated aluminas, magnesium oxide, talc, nickel oxide, iron oxides, cerium oxide, doped cerium oxide, oxides of perovskite structure, compounds comprising titanium of the type La 4 Sr 8 Ti 11 Mn 1-x Ga x O 38  with 0≦x≦1 and La 4 Sr 8 Ti 12-n M n O 38  with 0≦n≦1, compounds of the type BaTiO 3 , BaZrO 3 , Pb(Mg 0.25 Nb 0.75 )O 3 , Ba(Zn 0.25 Nb 0.75 )O 3 , Pb(Zn 0.25 Nb 0.75 )O 3 , PbTiO 3 , CaCu 3 Ti 4 O 12 , compounds of the bimevox-type structure, compounds of the lamox-type structure, compounds of the type SrCe 1-x M x O 3  with 0≦x≦1 and M being a rare-earth metal, compounds of the type BaCe 1-x M x O 3  with 0≦x≦1 and M being a rare-earth metal, compounds of the family La x Sr 1-x ScO 3  with 0≦x≦1, zeolites of structure Na x1 Ca x2 Mg x3 Ba x4 K x5 Al x6 (Si x7 O x8 ),x9H 2 O, x1 to x9 being positive integers or zero satisfying the following conditions: x6>0, x7>0, x8>0, x9>0 and x1+x2+x3+x4+x5>0, silicon carbide, silicon nitride, boron nitride, boron carbide, tungsten carbide, molybdenum disilicide MoSi 2  and titanium boride TiB 2 , and mixtures thereof, a catalytic coating comprising or formed from a catalyst material chosen from metals, preferably iron Fe, cobalt Co, nickel Ni, molybdenum Mo, copper Cu, ruthenium Ru, rhodium Rh, platinum Pt, palladium Pd, gold Au, silver Ag, iridium Ir, osmium Os, rhenium Re, and mixtures thereof, oxides, preferably oxides of scandium Sc, titanium Ti, vanadium V, chromium Cr, cobalt Co, copper Cu, palladium Pd, molybdenum Mo, iron Fe, nickel Ni, tungsten W, rhenium Re, oxides of perovskite structure, oxides of fluorite structure, zeolites, lanthanide oxides, preferably CeO 2 , and mixtures thereof, carbides, oxycarbides of formula (carbide) 1-x O x , with 0<x<1, and mixtures thereof, and mixtures thereof; a catalytic coating being a coating comprising or formed from a catalyst material known for catalysing a chemical reaction. 
     
     
         13 . A manufacturing method, comprising the following successive steps:
 preparation of a slip that is suitable for the manufacture of a porous product according to  claim 1 , and comprising, as a volume percentage, more than 4% of a powder of ceramic particles suspended in an aqueous liquid phase, said liquid phase comprising a crystal growth activator, p 1  optionally, pouring of the slip into a mould and/or removal of air bubbles contained in the slip,   oriented freezing of the slip so as to form a block comprising an assembly of ice crystals each having an elongated frustoconical tubular shape,   optionally, stripping of said block of frozen slip from the mould,   removal of the ice crystals from said frozen block of slip, optionally stripped from the mould, preferably by sublimation, so as to obtain a porous preform,   optionally, removal of binder from the porous preform obtained at the end of step e),   optionally, sintering of the porous preform obtained at the end of step e) or f) so as to obtain a porous sintered product,   optionally, machining and impregnation of said porous sintered product, in which method, in step a),   zirconium acetate and/or one or more zirconium acetate precursors are added to the slip in an amount such that a concentration of zirconium provided by the zirconium acetate is in a range from 14 g/l to 170 g/l of aqueous liquid phase; and   the powder of ceramic particles is introduced into the aqueous liquid phase after introduction of the zirconium acetate or zirconium acetate precursor(s); and a pH of the slip is adjusted a range from 2.75 to 5; and   an amount of powder of ceramic particles in the slip is less than 50% by volume; and   in which, in step c), a speed of a solidification front ranges from 40 μm/s to 400 μm/s.   
     
     
         14 . A product that is manufactured or that may have been manufactured according to a method according to  claim 13 . 
     
     
         15 . A device chosen from a ceramic electrochemical cell, a fuel cell, and in particular an SOFC cell, an IT-SOFC cell, a PCFC cell, a single-chamber fuel cell, a filtration element of a liquid or gaseous fluid, a storage microstructure used for storing a substance in the pores, a catalyst support, a heat exchanger, a heat insulator, a fluid distributor for conveying said fluid, and especially a gas distributor, a drop separator or a trickle block for an air processing plant, a battery, and especially a battery electrolyte, a supercapacitor, a moisture adsorber, a combustion microchamber, the said device comprising a product according to  claim 1 .